[117.01] Tracing the Dynamics of the Galactic Disk with SIM PlanetQuest

S. R. Majewski, P. M. Frinchaboy, R. J. Patterson (Univ. of Virginia)

Establishing the rotation curve of the Milky Way on an
absolute scale is one of the fundamental contributions that
SIM PlanetQuest can make to understanding the Galaxy and its
mass distribution. As preparatory work for the ``Taking
Measure of the Milky Way'' SIM Key Project, we have
undertaken a systematic spectroscopic survey of open star
clusters which can serve as tracers of Galactic disk
dynamics. We report progress on our inital sample of over
100 clusters for which the Hydra multifiber spectrographs on
the WIYN and Blanco telescopes have delivered ~1 km
s-1 radial velocities (RVs) of many dozens of stars per
cluster. The RVs are used to derive cluster membership for
individual stars in these crowded fields and to derive a
bulk cluster RV. The clusters selected for study have a
broad spatial distribution in order to be sensitive to the
disk velocity field in all Galactic quadrants and across a
Galactocentric radius range as much as 2.5 kpc from the
solar circle. These clusters already have published ages,
distances, and metallicity estimates, but these can be
improved once chemical abundances on a uniform scale are
measured from the homogenous spectra, and once SIM
parallaxes are obtained for member stars. The new RVs
combined with Tycho proper motions (for bright members in
each cluster) allow an initial investigation of the local
disk dynamics, but this will be substantially improved once
SIM proper motions are obtained for these and even more
distant open clusters.

We acknowledge funding by NASA/JPL contract 1228235, NSF
grant AST-0307851, and the F.H. Levinson Fund of the
Peninsula Community Foundation. PMF is supported by a
NASA-GSRP, a UVa Faculty Senate Dissertation-Year
Fellowship, and the Virginia Space Grant Consortium.